Cell surface molecules play important roles in regulation, differentiation and development. They can also be used to manipulate the human chromosomal content of human X Chinese hamster somatic cell hybrids. Immunological analysis of cell surface molecules influenced by genes on chromosome 21 will be identified and characterized using monoclonal antibodies. Deletion and irradiation hybrids will be isolated and used foro regional gene mapping of chromosome 21. Further studies will be undertaken on the analysis of the interferon system and the interaction of genes on chromosome 21. Comparative mapping provides a means for studying genome organization and chromosomal evolution. A gene map for chimpanzee chromosome 22 will be established and compared with its homologous human chromosome 21. A long term goal of these studies is to identify chromosome 21 encoded cell surface molecules which may plan a role in the pathogenesis of Down Syndrome.